Phase Diagram of Gelatin Plasticized by Water and Glycerol |
| |
Authors: | Mara Coppola Madeleine Djabourov Maria Ferrand |
| |
Institution: | 1. Laboratoire de Physique Thermique, ESPCI, 10 Rue Vauquelin, 75231 Paris Cedex 05, France;2. Capsugel, 10 Rue Timken, 68027 Colmar, France |
| |
Abstract: | Summary: Gelatin is widely used in capsules manufacturing. Most of the capsules in pharmaceutical applications are hard capsules made out of concentrated solutions of gelatin, where water has been progressively removed during the drying process. More recently soft capsules found an increasing interest in pharmaceutical and cosmetic applications where they are filled and sealed with a liquid substance. In order to keep the shells of capsules flexible after drying at room temperature, plasticizer is added to the gelatin aqueous solutions. We present in this paper a systematic investigation of gelatin films, equilibrated under a range of relative humidity (RH). The films contain glycerol as plasticizer P or only water and gelatin, (G). In order to analyze the role of the plasticizer, we fixed various P/G ratios and measured the water retention versus RH. Films were characterized by DSC (Mettler Toledo DSC823). Glass transition temperature Tg, melting temperature Tm and enthalpy associated with helix-coil transition were determined. The role of water and glycerol was examined in relation with the large variations of these transition temperatures with film composition. Non equilibrium effects are also discussed, in particular concerning the glass transition temperature, the relaxation effects and the water repartition between amorphous coils and helical structure. In conclusion, we propose a unique phase diagram of the gelatin films with any proportion of water and glycerol. |
| |
Keywords: | enthalpy helix-coil gelatin films glass transition glycerol plasticizer melting temperature |
|
|